Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$124.27	6.855%	$132.7887	$132.79	$132.80	$132.80
Purchase #2	$37.73	7.300%	$40.4843	$40.48	$40.50	$40.50
Purchase #3	$153.26	12.819%	$172.9064	$172.91	$172.90	$172.90
Purchase #4	$191.94	3.629%	$198.9055	$198.91	$198.90	$198.90
Purchase #5	$195.30	11.825%	$218.3942	$218.39	$218.40	$218.40
Purchase #6	$218.29	13.367%	$247.4688	$247.47	$247.45	$247.50
Purchase #7	$145.71	11.314%	$162.1956	$162.20	$162.20	$162.20
7 purchase totals =	$1,066.50		$1,173.1435	$1,173.15	$1,173.15	$1,173.20